a(n) = 5^n*cos(2*n*arctan(1/2)) or denominator of tan(2*n*arctan(1/2)).

A066771

a(n) = 5^n*cos(2*n*arctan(1/2)) or denominator of tan(2*n*arctan(1/2)).

Terms

    a(0) =1a(1) =3a(2) =-7a(3) =-117a(4) =-527a(5) =-237a(6) =11753a(7) =76443a(8) =164833a(9) =-922077a(10) =-9653287a(11) =-34867797a(12) =32125393a(13) =1064447283a(14) =5583548873a(15) =6890111163a(16) =-98248054847a(17) =-761741108157

External references